drag the bell bag in your inventory to your bell balance, it should add to it. Also tapping your bells will bring up a selection menu so you can pick the amount to drop.

As for planting the money, I'm not sure how correct I am about this but I think you just bury the bag of money anywhere and based on how much money you buried it has a set chance of growing or not. There's a FAQ on gamefaqs with more info.